Preheat oven to 350 degrees F. Place 3/4 cup of Enchilada sauce in the bottom of a rectangular baking dish (at least 8x12 inches). Set aside.
Add the cubed sweet potato into a medium pot of water and bring to a boil. Reduce heat and simmer for 9 to 15 minutes, uncovered, until fork tender. Drain and set aside.
In a large skillet, add the oil, onion, red pepper and garlic and sauté over medium heat for around 3 to 5 minutes until the onion softens.
Add in the spinach, and black beans to the sweet potato mixture. Cook for an additional 3 to 5 minutes over medium-high heat, until the spinach is wilted.
Stir in 1/2 cup of enchilada sauce, followed by the lime juice, chili powder, cumin, and salt.
Scoop 3/4 cup of the sweet potato and black bean filling onto each tortilla. Roll up the tortilla and place it, seam side down, in the casserole dish. Repeat for the rest. If you have any leftover filling, you can spread it on top of the tortillas. Spread all of the remaining enchilada sauce on top of the tortillas until they are completely covered in sauce.
Bake the enchiladas, uncovered, for 20 to 25 minutes, until the enchiladas are heated through.
While the enchiladas are baking, prepare the Avocado Crema.